Automatic shift preselection mode for mechanical transmission system with semi-automatic shift implementation

ABSTRACT

A control system (104) for semi-automatically executing automatically and manually selected upshifts and downshifts of a mechanical transmission system (10) is provided. The control system includes a central processing unit (106) for receiving input signals indicative of transmission input shaft (16) and output shaft (90) speeds and from a driver control console (108) indicative of manual selection of upshifts or downshifts from a currently engaged gear ratio, or manual selection of operation in an automatic preselect mode, and processing the same in accordance with predetermined logic rules to issue command output signals to a transmission actuator (112, 70, 96) to implement the selected shifts upon a manually caused torque break of the transmission and manual substantial synchronization of the transmission in the selected ratio thereafter.

RELATED APPLICATIONS

This Application is related to U.S. application Ser. No. 368,011, titledSEMI-AUTOMATIC SHIFT IMPLEMENTATION FOR MECHANICAL TRANSMISSION SYSTEM;application Ser. No. 368,502, titled CONTROL SYSTEM AND METHOD FORSENSING AND INDICATING NEUTRAL IN A SEMI-AUTOMATIC MECHANICALTRANSMISSION SYSTEM; application Ser. No. 368,492, titled ENHANCEDMISSED SHIFT RECOVERY FOR SEMI-AUTOMATIC SHIFT IMPLEMENTATION CONTROLSYSTEM; and application Ser. No. 368,500, titled CONTROL SYSTEM/METHODFOR CONTROLLING SHIFTING OF A RANGE TYPE COMPOUND TRANSMISSION USINGINPUT SHAFT AND MAINSHAFT SPEED SENSORS now U.S. Pat. No. 4,991,099; allassigned to Eaton Corporation, the assignee of this Application, and allfiled the same day as this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to vehicular semi-automatic mechanicaltransmission systems and, in particular, to semi-automatic mechanicaltransmission systems of the type providing partially automaticimplementation of preselected shifting of mechanical transmission gearratios and having at least one mode of operation wherein the shifting ofratio changes are automatically preselected by the system centralprocessing unit.

2. Description of the Prior Art

Fully automatic transmission systems, both for heavy-duty vehicles suchas heavy-duty trucks, and for automobiles, that sense throttle openingsor positions, vehicle speeds, engine speeds, and the like, andautomatically shift the vehicle transmission in accordance therewith,are well known in the prior art. Such fully automatic change geartransmission systems include automated transmissions wherein pressurizedfluid is utilized to frictionally engage one or more members to othermembers or to a ground to achieve a selected gear ratio as well asautomated mechanical transmissions utilizing electronic and/or pneumaticlogic and actuators to engage and disengage mechanical (i.e. positive)clutches to achieve a desired gear ratio. Examples of such transmissionsmay be seen by reference to U.S. Pat. Nos. 3,961,546; 4,081,065 and4,361,060, the disclosures of which are hereby incorporated byreference.

Such fully automatic change gear transmissions can be unacceptablyexpensive, particularly for the largest heavy-duty vehicles which arenot typically sold in high volumes. Additionally, those automatic changegear transmissions utilizing pressurized fluid and/or torque converterstend to be relatively inefficient in terms of power dissipated betweenthe input and output shafts thereof.

Semi-automatic transmission systems utilizing electronic control unitswhich sense throttle position, engine, input shaft, output shaft and/orvehicle speed, and utilize automatically controlled fuel throttledevices, gear shifting devices and/or master clutch operating devices tosubstantially fully automatically implement operator manually selectedtransmission ratio changes are known in the prior. Examples of suchsemi-automatic transmission systems may be seen by reference to U.S.Pat. Nos. 4,425,620; 4,631,679 and 4,648,290, the disclosures of whichare incorporated herein by reference.

While such semi-automatic mechanical transmission systems are very wellreceived as they are somewhat less expensive than fully automatictransmission systems, allow manual clutch control for low speedoperation and/or do not require automatic selection of the operatinggear ratio, they may be too expensive for certain applications as arelatively large number of sensors and automatically controllableactuators, such as a master clutch and/or a fuel throttle deviceactuator, are required to be provided, installed and maintained.

SUMMARY OF THE INVENTION

In accordance with the present invention, the drawbacks of the prior artare overcome or minimized by the provision of a semi-automatic shiftimplementation system/method for a mechanical transmission system foruse in vehicles having a manually only controlled engine throttle means,and a manually only controlled master clutch. The system has at leastone mode of operation wherein the shifts to be semi-automaticallyimplemented are automatically preselected and includes a control/displaypanel or console for operator selection of operation in the automaticpreselection mode and indication of automatic preselection of upshifts,downshifts or shifts into neutral. An electronic control unit (ECU) isprovided for receiving input signals indicative of transmission inputand output shaft speeds and for processing same in accordance withpredetermined logic rules to determine if an upshift or downshift fromthe currently engaged ratio is required and to issue command outputsignals to a transmission actuator for shifting the transmission inaccordance with the command output signals.

The control/display device will display the selected but not yetimplemented shift as well as the current status of the transmission,and, preferably will allow the operator to select/preselect a shift intoa higher ratio, a lower ratio or into neutral. Preferably, the controldevice will also allow a manually or an automatically preselected shiftto be cancelled.

Accordingly, a control system/method for a vehicular semi-automaticmechanical transmission system for partially automatic implementation ofautomatically selected transmission shifts is provided which does notrequire throttle or clutch actuators, and which requires only two speedsignal inputs, is provided.

This and other objects and advantages of the present invention willbecome apparent from a reading of the detailed description of thepreferred embodiment taken in connection with the attache drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the vehicular mechanicaltransmission system partially automated by the system of the presentinvention.

FIG. 1A is a schematic illustration of the shift pattern of thetransmission of FIG. 1.

FIG. 2 is a schematic illustration of the automatic preselect andsemi-automatic shift implementation system for a mechanical transmissionsystem of the present invention.

FIG. 3 is a schematic illustration of an alternate control console forthe system of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Certain terminology will be used in the following description forconvenience in reference only and will not be limiting. The words"upwardly", "downwardly", "rightwardly", and "leftwardly" will designatedirections in the drawings to which reference is made. The words"forward", "rearward", will refer respectively to the front and rearends of the transmission as conventionally mounted in a vehicle, beingrespectfully from left and right sides of the transmission asillustrated in FIG. 1. The words "inwardly" and "outwardly" will referto directions toward and away from, respectively, the geometric centerof the device and designated parts thereof. Said terminology willinclude the words above specifically mentioned, derivatives thereof andwords of similar import.

The term "compound transmission" is used to designate a change speed orchange gear transmission having a multiple forward speed maintransmission section and a multiple speed auxiliary transmission sectionconnected in series whereby the selected gear reduction in the maintransmission section may be compounded by further selected gearreduction in the auxiliary transmission section. "Synchronized clutchassembly" and words of similar import shall designate a clutch assemblyutilized to nonrotatably couple a selected gear to a shaft by means of apositive clutch in which attempted engagement of said clutch isprevented until the members of the clutch are at substantiallysynchronous rotation in a relatively large capacity friction means areutilized with the clutch members and are sufficient, upon initiation ofa clutch engagement, to cause the clutch members and all membersrotating therewith to rotate and substantially synchronous speed.

The term "upshift" as used herein, shall mean the shifting from a lowerspeed gear ratio into a higher speed gear ratio. The term "downshift" asused herein, shall mean the shifting from a higher speed gear ratio to alower speed gear ratio. The terms "low speed gear", "low gear" and/or"first gear" as used herein, shall all designate the gear ratio utilizedfor lowest forward speed operation in a transmission or transmissionsection, i.e., that set of gears having the highest ratio of reductionrelative to the input shaft of the transmission.

A "selected direction" of shifting will refer to selection of eithersingle or multiple upshifting or downshifting from a particular gearratio.

Referring to FIG. 1, a range type compound transmission 10 of the typepartially automated by the semi-automatic mechanical transmission systemhaving an automatic preselect mode of operation of the present inventionis illustrated. Compound transmission 10 comprises a multiple speed maintransmission section 12 connected in series with a range type auxiliarysection 14. Transmission 10 is housed within a housing H and includes aninput shaft 16 driven by a prime mover such as diesel engine E through aselectively disengaged, normally engaged friction master clutch C havingan input or driving portion 18 drivingly connected to the enginecrankshaft 20 and a driven portion 22 rotatably fixed to thetransmission input shaft 16.

The engine E is fuel throttle controlled by a manually controlledthrottle device (not shown) and the master clutch C is manuallycontrolled by a clutch pedal (not shown) or the like. An input shaftbrake B, operated by overtravel depression of the clutch pedal, ispreferably provided to provide quicker upshifting as is well known inthe prior art.

Transmissions similar to mechanical transmission 10 are well known inthe prior art and may be appreciated by reference to U.S. Pat. Nos.3,105,395; 3,283,613 and 4,754,665, the disclosures of which areincorporated by reference.

In main transmission section 12, the input shaft 16 carries an inputgear 24 for simultaneously driving a plurality of substantiallyidentical countershaft assemblies 26 and 26A at substantially identicalrotational speeds. The two substantially identical countershaftassemblies are provided on diametrically opposite sides of mainshaft 28which is generally coaxially aligned with the input shaft 16. Each ofthe countershaft assemblies comprises a countershaft 30 supported bybearings 32 and 34 in housing H, only a portion of which isschematically illustrated. Each of the countershafts is provided with anidentical grouping of countershaft gears 38, 40, 42, 44, 46 and 48,fixed for rotation therewith. A plurality of mainshaft gears 50, 52, 54,56 and 58 surround the mainshaft 28 and are selectively clutchable, oneat a time, to the mainshaft 28 for rotation therewith by sliding clutchcollars 60, 62 and 64 as is well known in the prior art. Clutch collar60 may also be utilized to clutch input gear 24 to mainshaft 28 toprovide a direct drive relationship between input shaft 16 and mainshaft28.

Typically, clutch collars 60, 62 and 64 are axially positioned by meansof shift forks associated with the shift housing assembly 70, as wellknown in the prior art. Clutch collars 60, 62 and 64 may be of the wellknown acting nonsynchronized double acting jaw clutch type.

Shift housing or actuator 70 is actuated by compressed fluid, such ascompressed air, and is of the type automatically controllable by acontrol unit as may be seen by reference to U.S. Pat. Nos. 4,445,393;4,555,959; 4,361,060; 4,722,237 and 2,931,237, the disclosures of whichare incorporated by reference.

Mainshaft gear 58 is the reverse gear and is in continuous meshingengagement with countershaft gears 48 by means of conventionalintermediate idler gears (not shown). It should also be noted that whilemain transmission section 12 does provide five selectable forward speedratios, the lowest forward speed ratio, namely that provided bydrivingly connecting mainshaft drive gear 56 to mainshaft 28, is oftenof such a high gear reduction it has to be considered a low or "creeper"gear which is utilized only for starting of a vehicle under severeconditions and, is not usually utilized in the high transmission range.Accordingly, while main transmission section 12 does provide fiveforward speeds, it is usually referred to as a "four plus one" mainsection as only four of the forward speeds are compounded by theauxiliary range transmission section 14 utilized therewith.

Jaw clutches 60, 62, and 64 are three-position clutches in that they maybe positioned in the centered, nonengaged position as illustrated, or ina fully rightwardly engaged or fully leftwardly engaged position bymeans of a shift lever 72. As is well known, only one of the clutches60, 62 and 64 is engageable at a given time and main section interlockmeans (not shown) are provided to lock the other clutches in the neutralcondition.

Auxiliary transmission range section 14 includes two substantiallyidentical auxiliary countershaft assemblies 74 and 74A, each comprisingan auxiliary countershaft 76 supported by bearings 78 and 80 in housingH and carrying two auxiliary section countershaft gears 82 and 84 forrotation therewith. Auxiliary countershaft gears 82 are constantlymeshed with and support range/output gear 86 while auxiliary sectioncountershaft gears 84 are constantly meshed with output gear 88 which isfixed to transmission output shaft 90.

A two-position synchronized jaw clutch assembly 92, which is axiallypositioned by means of a shift fork (not shown) and the range sectionshifting actuator assembly 96, is provided for clutching either gear 86to mainshaft 28 for low range operation or gear 88 to mainshaft 28 fordirect or high range operation of the compound transmission 10. The"shift pattern" for compound range type transmission 10 is schematicallyillustrated in FIG. 1A.

Range section actuator 96 may be of the type illustrated in U.S. Pat.Nos. 3,648,546; 4,440,037 and 4,614,126, the disclosures of which arehereby incorporated by reference.

Although the range type auxiliary section 14 is illustrated as atwo-speed section utilizing spur or helical type gearing, it isunderstood that the present invention is also applicable to range typetransmissions utilizing combined splitter/range type auxiliary sections,having three or more selectable range ratios and/or utilizing planetarytype gearing. Also, any one or more of clutches 60, 62 or 64 may be ofthe synchronized jaw clutch type and transmission sections 12 and/or 14may be of the single countershift type.

For purposes of providing the automatic preselect mode of operation andthe semi-automatic shift implementation operation of transmission 10, aninput shaft speed sensor and an output shaft speed sensor 100 areutilized. Alternatively to output shaft speed sensor 100, a sensor 102for sensing the rotational speed of auxiliary section countershaft gear82 may be utilized. The rotational speed of gear 82 is, of course, aknown function of the rotational speed of mainshaft 28 and, if clutch 92is engaged in a known position, a function of the rotational speed ofoutput shaft 90.

The automatic preselect and semi-automatic shift implementation controlsystem 104 for a mechanical transmission system of the present inventionis schematically illustrated in FIG. 2. Control system 104, in additionto the mechanical transmission system 10 described above, includes anelectronic control unit 106, preferably microprocessor based, forreceiving input signals from the input shaft speed sensor 98, from theoutput shaft speed sensor 100 (or, alternatively, the mainshaft speedsensor 102) and from the driver control console 108. The ECU 106 mayalso receive inputs from an auxiliary section position sensor 110.

The ECU is effective to process the inputs in accordance withpredetermined logic rules to issue command output signals to atransmission operator, such as solenoid manifold 112 which controls themainsection section actuator 70 and the auxiliary section actuator 96,and to the driver control counsel 108.

In the preferred embodiment, the driver control counsel allows theoperator to manually select a shift in a given direction or to neutralfrom the currently engaged ratio, or to select a semi-automaticpreselect mode of operation, and provides a display for informing theoperator of the current mode of operation (automatic or manualpreselection of shifting), the current transmission operation condition(forward, reverse or neutral) and of any ratio change or shift (upshift,downshift or shift to neutral) which has been preselected but not yetimplemented.

Console 108 includes three indicator lights 114, 116 and 118 which willbe lit to indicate that the transmission 10 is in a forward drive,neutral or reverse drive, respectively, condition. The console alsoincludes three selectively lighted pushbuttons 120, 122, and 124 whichallow the operator to select an upshift, automatic preselection mode ora downshift, respectively. A pushbutton 126 allows selection of a shiftinto neutral.

A selection made by depressing or pushing any one of buttons 120, 122,124 or 126, and may be cancelled (prior to execution in the case ofbuttons 120, 124 and 126) by redepressing the buttons. Of course, thebuttons and lighted buttons can be replaced by other selection means,such as a toggle switch and/or a toggle switch and light or otherindicia member. A separate button or switch for selection of reverse maybe provided or reverse may be selected as a downshift from neutral.Also, neutral may be selected as an upshift from reverse or as adownshift from low.

In operation, to select upshifts and downshifts manually, the operatorwill depress either button 120 or button 124 as appropriate. Theselected button will then be lighted until the selected shift isimplemented or until the selection is cancelled.

To implement a selected shift, the manifold 112 is preselected to causeactuator 70 to be biased to shift main transmission section 12 intoneutral. This is accomplished by the operator causing a torque break bymanually momentarily decreasing and/or increasing the supply of fuel tothe engine and/or manually disengaging the master clutch C. As thetransmission is shifted into neutral, and neutral is verified by theECU, the neutral condition indicia button 116 is lighted. If theselected shift is a compound shift, i.e. a shift of both the mainsection 12 and of the range section 14, such as a shift from 4th to 5thspeeds as seen in FIG. 1A, the ECU will issue command output signals tomanifold 112 to cause the auxiliary section actuator 96 to complete therange shift.

When the range auxiliary section is engaged in the proper ratio, the ECUwill calculate or otherwise determine, and continue to update, anenabling range or band of input shaft speeds, based upon sensed outputshaft (vehicle) speed and the ratio to be engaged, which will result inan acceptably synchronous engagement of the ratio to be engaged. As theoperator, by throttle manipulation and/or use of the input shaft brake,causes the input shaft speed to fall within the acceptable range, theECU 106 will issue command output signals to manifold 112 to causeactuator 70 to engage the mainsection ratio to be engaged. Preferably,the actuator will respond very quickly not requiring the operator tomaintain the input shaft speed within the acceptable range for anextended period of time. To select a shift into transmission neutral,selection button 126 is pushed. Indicating light 116 will flash untilthe ECU confirms that neutral is obtained at which time the light 116will assume a continuously lighted condition while the transmissionremains in neutral.

In the automatic preselection mode of operation, selected by use oflighted pushbutton 122, the ECU will, based upon stored logic rules,currently engaged ratio (which may be calculated by comparing inputshaft to output shaft speed) and output shaft or vehicle speed,determine if an upshift or a downshift is required and preselect same.The operator is informed that an upshift or downshift is preselected andwill be semi-automatically implemented by a command output signal fromECU 106 causing either lighted pushbutton 120 or lighted pushbutton 124to flash. The operator may initiate semi-automatic implementation of theautomatically preselected shift as indicated above or may cancel theautomatic mode and the shift preselected thereby by depression ofpushbutton 122.

As an alternative, the neutral condition indication light 116 may beeliminated and neutral selection pushbutton 126 replaced by a lightedpushbutton.

An alternate driver control and display console 130 may be seen byreference to FIG. 3. A joy stick 132 is movable against a resilient biasfrom its centered position to select upshifts, downshifts, a shift toneutral or the automatic preselect mode by movement up, down, leftwardor rightward, respectively, as indicated. Indicia lights 134 and 136 arelighted to indicate an upshift or downshift, respectively, ispreselected. Indicia lights 138 and 140, respectively, are lighted toindicate a vehicle forward or reverse, respectively, mode of operation.Indicia light 142 is steadily lighted to indicate a transmission neutralcondition and is flashed to indicate a preselected but not yet confirmedneutral condition. Indicia light 144 is lighted to indicate system 104is operating in the automatic preselection mode of operation.

Accordingly, it may be seen that a relatively simple and inexpensivesemi-automatic shift implementation control system (104)/method for amechanical transmission system 10 having an automatic preselect mode ofoperation and requiring only a transmission shift actuator (112/70/96)and two speed inputs to be added to vehicle mechanical transmissionsystem is provided. An electronic control unit 106 for receiving the twospeed inputs, and inputs from an operator's console and for issuingcommand outsignals to the actuators and to the display portion of theoperator's console is also provided. The system semi-automaticallyexecutes manually or automatically preselected shifts requiring theoperator to (i) cause a torque break for disengaging the currentlyengaged ratio and (ii) to cause substantially synchronous rotation forengagement of the selected ratio, which allows the system to operatewithout requiring automatically operated throttle controls or masterclutch actuators.

Although the present invention has been described with a certain degreeof particularity, it is understood that various changes to form anddetail may be made without departing from the spirit and the scope ofthe invention as hereinafter claimed.

I claim:
 1. A control system (104) for semi-automatic implementation of automatically selected shifts of a mechanical change gear transmission system comprising a manually controlled fuel throttle controlled engine (E), a multi-speed change gear mechanical transmission (10), a manually controlled master friction clutch (C) drivingly interposed between the engine and the transmission, a first sensor (98) for providing a first input signal indicative of transmission input shaft (16) rotational speed, a second sensor (100) for providing a second input signal indicative of the rotational speed of a transmission shaft (90) independently rotatable relative to the transmission input shaft under at least certain transmission operating conditions and a non-manually controllable transmission actuator (112, 70, 96) for controlling shifting of the transmission, said control system characterized by;indicia means (120, 124) for providing an indication of a selection but not yet confirmation of an upshift or a downshift from a currently engaged transmission ratio or from neutral to a selected ratio: a central processing unit (106) for receiving said input signals and for processing the same in accordance with predetermined logic rules to issue command output signals, said central processing unit including;(a) means for determining the desirability of a shift from a currently engaged ratio, to select such a shift if desirable and for issuing command output signals to said indicia means to provide an indication that an upshift or a downshift, as appropriate, has been selected; (b) means responsive to a selection of a transmission shift from a currently engaged ratio for issuing command output signals to said actuator to bias the transmission to be shifted into neutral; (c) means responsive to (i) a selection of a shift from a currently engaged ratio into a selected ratio and (ii) confirmation of a transmission neutral condition for (i) sensing manual substantial synchronization of the transmission and (ii) thereafter for issuing command output signals to said actuator to cause the transmission to be shifted into the selected ratio; and (d) means for confirming a selected shift has been implemented and for issuing command output signals to said indicia means to terminate the indication of a selected shift.
 2. The control system of claim 1 wherein said second input signal is continuously indicative of the speed of the transmission output shaft (96).
 3. The control system of claims 1 or 2 wherein said means for sensing manual synchronization comprises means for determining a reference range of acceptable values of said first signal as a function of said second signal and means for comparing the current value of said first signal to said range of reference values.
 4. The control system of claims 1 or 2 additionally comprising means allowing a selection to be manually cancelled.
 5. The control system of claims 1 or 2 additionally comprising means allowing a selection to be manually cancelled.
 6. A control system (104) for semi-automatic implementation of manually and automatically selected shifts of a mechanical change gear transmission system comprising a manually controlled fuel throttle controlled engine (E), a multi-speed change gear mechanical transmission (10), a manually controlled master friction clutch (C) drivingly interposed between the engine and the transmission, a first sensor (98) for providing a first input signal indicative of transmission input shaft (16) rotational speed, a second sensor (100) for providing a second input signal indicative of the rotational speed of a transmission shaft (90) independently rotatable relative to the transmission input shaft under at least certain transmission operating conditions and a non-manually controllable transmission actuator (112, 70, 96) for controlling shifting of the transmission, said control system characterized by;means (120, 122, 124/132) for manually selecting an upshift or a downshift from a currently engaged transmission ratio or from neutral to a selected ratio and for manually selecting operation in an automatic preselect mode, and providing a third input signal indicative of said selection; indicia means (120, 122, 124) for indicating a selection of the automatic preselect mode and for indicating selection but not confirmed execution of a shift from the currently engaged transmission ratio; a central processing unit (106) for receiving said first, second and third input signals and for processing the same in accordance with predetermined logic rules to issue command output signals, said central processing unit including; (a) means responsive to manual selection of operation in an automatic mode (i) for issuing a command output signal to said indicia means to indicate that the automatic preselect mode has been selected, (ii) for determining the desirability of a shift from the currently engaged ratio and to select such a shift if desirable and (iii) for issuing command output signals to said indicia means to provide an indication that an upshift or downshift, as appropriate, has been selected; (b) means responsive to a selection of a transmission shift from a currently engaged ratio for issuing command output signals to said actuator to bias the transmission to be shifted into neutral; (c) means responsive to (i) a selection of a shift from a currently engaged ratio into a selected ratio and (ii) confirmation of a transmission neutral condition for (i) sensing manual substantial synchronization of the transmission and (ii) thereafter for issuing command output signals to said actuator to cause the transmission to be shifted into the selected ratio. (d) means for confirming execution of a selected shift and for issuing command output signals to said indicia means to terminate the indication of a selected shift.
 7. The control system of claim 6 wherein said means for manually selecting additionally includes means (126/132) for manually selecting a shift directly into neutral from any currently engaged ratio.
 8. The control system of claim 7 wherein said second input signal is continuously indicative of the speed of the transmission output shaft (96).
 9. The control system of claim 6 wherein said second input signal is continuously indicative of the speed of the transmission output shaft (96).
 10. The control system of claims 6, 7, 9 or 8 wherein said means for sensing manual synchronization comprises means for determining a reference range of acceptable values of said first signal as a function of said second signal and means for comparing the current value of said first signal to said range of reference values.
 11. The control system of claim 10 additionally comprising indicia means for indicating the current status of the transmission.
 12. The control system of claim 10 wherein said means for manually selecting allows a manual selection to be manually cancelled.
 13. The control system of claims 6, 7, 9 or 8 additionally including indicia means (114, 116, 118/138, 140, 142) for indicating the current status (FOR, NEUT, REV) of the transmission.
 14. The control system of claims 6, 7, 9 or 8 wherein said means for selecting allows a selection to be manually cancelled.
 15. The control system of claims 6, 7, 9 or 8 wherein said actuator is operated by pressurized compressed fluid.
 16. The control system of claims 6, 7, 9 or 8 wherein said central processing unit (106) is microprocessor based.
 17. The control system of claims 6, 7, 9, or 8 wherein said means for manually selecting comprise push buttons.
 18. The control system of claim 17 wherein said push buttons are lighted push buttons, said processing unit issuing command output signals causing said push buttons to be lighted upon selection of an upshift or a downshift from the currently engaged ratio and to remain constantly or intermittently lighted until execution of the selected shift is confirmed.
 19. The control system of claims 6, 7, 9, or 8 wherein said indicia means are lights.
 20. The control system of claim 19 wherein said lights are constantly lit to indicate a manually selected shift from the currently engaged transmission ratio and are rapidly lit and unlit to indicate an automatically selected shift from the currently engaged transmission ratio.
 21. A control system (104) for semi-automatic implementation of automatically selected shifts of a mechanical change gear transmission system comprising a fuel throttle controlled engine (E), a mutli-speed change gear mechanical transmission (10), a manually controlled master friction clutch (C) drivingly interposed between the engine and the transmission, a first sensor (98) for providing a first input signal indicative of transmission input shaft (16) rotational speed, a second sensor (100) for providing a second input signal indicative of the rotational speed of a transmission shaft (90) independently rotatable relative to the transmission input shaft under at least certain transmission operating conditions and a non-manually controllable transmission actuator (112, 70, 96) for controlling shifting of the transmission, said control system characterized by;indicia means (120, 124) for providing an indication of a selection but not yet confirmation of an upshift or a downshift from a currently engaged transmission ratio or from neutral to a selected ratio; a central processing unit (106) for receiving said input signals and for processing the same in accordance with predetermined logic rules to issue command output signals, said central processing unit including;(a) means for determining the desirability of a shift from a currently engaged ratio, to select such a shift if desirable and for issuing command output signals to said indicia means to provide an indication that an upshift or a downshift, as appropriate, has been selected; (b) means responsive to a selection of a transmission shift from a currently engaged ratio for issuing command output signals to said actuator to bias the transmission to be shifted into neutral; (c) means responsive to (i) a selection of a shift from a currently engaged ratio into a selected ratio and (ii) confirmation of a transmission neutral condition for (i) sensing substantial synchronization of the transmission and (ii) thereafter for issuing command output signals to said actuator to cause the transmission to be shifted into the selected ratio; and (d) means for confirming a selected shift has been implemented and for issuing command output signals to said indicia means to terminate the indication of a selected shift.
 22. The control system of claim 21 wherein said second input signal is continuously indicative of the speed of the transmission output shaft (90).
 23. The control system of claims 21 or 22 wherein said means for sensing synchronization comprises means for determining a reference range of acceptable values of said first signal as a function of said second signal and means for comparing the current value of said first signal to said range of reference values. 